Optical ranging instruments are known, which direct a time-modulated light beam in the direction toward a target object, the distance of which from the measuring instrument should be established. The returning light, reflected or scattered by the targeted target object, is at least partly detected by the instrument and used to establish the distance to be measured. Here, a typical measurement range lies in a range of distances from a few centimeters to several 100 meters.
In order to be able to measure the distance to the target object using a light beam, the light beam is e.g. modulated in time in terms of its intensity. By way of example, light pulses can be emitted and a run-time of a light pulse from the emission to the detection can be measured and the distance to the target object can be calculated therefrom. However, very short light pulses have to be emitted for this purpose and very fast detection electronics have to be used in order to be able to obtain sufficiently accurate measurement results. Alternatively, the intensity of a light beam can be modulated periodically in time and a phase shift between the emitted and the detected light signal can be used to determine the run-time and hence the distance to the target object. The principle of laser distance measurement is generally known by the phrase “time-of-flight ranging”, for example with continuous modulation of the intensity of the laser beam.
DE 198 04 050 A1 has disclosed a ranging instrument with a laser diode and photodiode for generating and receiving an optical transmission or reception measurement signal. In order to carry out a calibration of the ranging instrument, the latter is provided with an adjustable reflecting flap which, during the calibration, is adjusted by an actuation drive in an optical path of the transmission measurement signal, as a result of which the transmission measurement signal is deflected and directly directed onto the photodiode via a reference path.
DE 10 2006 013 290 A1 discloses a device for optical ranging, in which a detector of a reception unit has a plurality of light-sensitive areas, which are separated from one another and can be activated separately from one another. Here, each of the light-sensitive areas has a photodiode, e.g. a PIN diode or an APD (avalanche photodiode), or a CCD chip as light-sensitive element. These light-sensitive elements establish an analog detection signal corresponding to an intensity of the received light. The light-sensitive areas can be activated in a selective manner and can in this fashion be combined to form an overall detection area, which can be adapted to the best possible extent to a portion of the detector area illuminated by a light source in order thus to improve a signal-to-noise ratio.